libavformat/avformat.h: Move docs inside of #if

Otherwise AVTimebaseSource gets av_apply_bitstream_filters' documentation in doxygen.
Signed-off-by: NMax Weber <mii7303@gmail.com>
Signed-off-by: NMichael Niedermayer <michael@niedermayer.cc>

libavformat/avformat.h

@@ -2954,6 +2954,7 @@ int avformat_match_stream_specifier(AVFormatContext *s, AVStream *st,
 
 int avformat_queue_attached_pictures(AVFormatContext *s);
 
+#if FF_API_OLD_BSF
 /**
  * Apply a list of bitstream filters to a packet.
  *
@@ -2965,7 +2966,6 @@ int avformat_queue_attached_pictures(AVFormatContext *s);
  * @return  >=0 on success;
  *          AVERROR code on failure
  */
-#if FF_API_OLD_BSF
 attribute_deprecated
 int av_apply_bitstream_filters(AVCodecContext *codec, AVPacket *pkt,
                                AVBitStreamFilterContext *bsfc);